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On Jun 7, 10:47*pm, wrote:
Due to the problems of getting 100LL *in many places, Lycoming is
seeking FAA approval for the standard compression engines to be able
to use 93 octane auto gas. Link to avweb article bellow. Sounds like
good news, since I have an O-360. Maybe airports will start to carry
it.

"Robert M. Gary" wrote in message
...
On Jun 7, 10:47 pm, wrote:
Due to the problems of getting 100LL in many places, Lycoming is
seeking FAA approval for the standard compression engines to be able
to use 93 octane auto gas. Link to avweb article bellow. Sounds like
good news, since I have an O-360. Maybe airports will start to carry
it.

On Jun 11, 7:21*pm, "Blueskies" wrote:
"Robert M. Gary" wrote in ...
On Jun 7, 10:47 pm, wrote:
Due to the problems of getting 100LL in many places, Lycoming is
seeking FAA approval for the standard compression engines to be able
to use 93 octane auto gas. Link to avweb article bellow. Sounds like
good news, since I have an O-360. Maybe airports will start to carry
it.http://www.avweb.com/avwebflash/news...AutoGasApprova...

Yep, and all you have to do is to fly to Europe to get ASTM D4814 gas.
I guess its not too far out of my way to get cheap gas

-Robert

We could just import it!

according to the article ASTM D4814 is the American standard, no? All
it really means is that 93 octane (88 aviation rating) auto gas that
doesn't have ethanol or something else in it is OK. Why else would
Lycoming be going to the trouble if it wasn't available here. If ASTM
D4814 isn't available now, it is almost certainly easier and cheaper
than avgas, which is far different than auto gas.

I'm curious where you got the 88 aviation octane number. If that is
accurate, O-360s and IO-360s will likely be blowing holes in the tops of
their pistons on hot days.

John Galban=====N4BQ (PA28-180)

Temp has almost nothing practical to do with the octane required. What
matters is the internal cylinder pressure. For example the IO-520 in my
Bo develops about 800 psi, sea level and standard day, at max rpm and
full throttle. The GAMI guys have instrumented aviation engines and
gathered this data. Neither Lyc or Continental have done so. At 800
psi the 520 is on the ragged edge of detonation. That's at 31 inches of
MP, what you'd get at sea level. They also determined that at 26 inches
of MP the 520 develops 400 psi. This is also why owners with constant
speed props are told to always reduce manifold pressure first. If you
are at 800 psi with everything wide open and you reduce rpm you have
made the situation worse. The engine stays at the high pressures
longer, and at a different spot relative to top dead center, because
you just made the engine turn slower. All bad. So the fact is that it
is the internal cylinder pressure that determines what octane you need.
While reading the article he wrote I got to thinking that I never see
over 26 inches of MP at my elevation of 3650 and of course the higher
you go the lower it gets. Therefore here at 3650 MSL 100 octane is not
needed, 90 would be more than adequate. And go to those mountain strips
that are higher yet and your octane requirement drops even lower.

On Jun 12, 12:13*pm, "JGalban via AviationKB.com" u32749@uwe wrote:
wrote:
All
it really means is that 93 octane (88 aviation rating) auto gas that
doesn't have ethanol or something else in it is OK.

* *Doesn't have ethanol? *I don't think so. *I read the spec and it has
provisions for oxygenates (ethanol by default). *Lyc. doesn't care if you
burn ethanol in the engine. *It's the plane's fuel system (tanks, hoses,
seals, etc...) that are most likely to have problems with it. *Lyc. is not
applying for airframe approvals, so that's not their problem.

* *I'm curious where you got the 88 aviation octane number. * If that is
accurate, O-360s and IO-360s will likely be blowing holes in the tops of
their pistons on hot days.

John Galban=====N4BQ (PA28-180)

--
Message posted viahttp://www.aviationkb.com

I got the octane info from a member of the Cardinal flyers group that
owns a turbo Cardinal. He works for Chevron and is very knowledgeable
about petroleum products. He has a digest column where he answers
questions from members about their planes.

Temp has almost nothing practical to do with the octane required. What
matters is the internal cylinder pressure.

I agree that cylinder pressure is the primary factor, but intake
temperatures can push detonation margins lower. That's why intercoolers and
water injection systems were invented.

Down here closer to sea level, when the official temp is 115F in the shade,
it's not unusual to have temps greater thatn 135F, 3ft. above superheated
asphalt. I've got two vehicles (truck and motorcycle) that are supposed to
run on 87 octane that will detonate lightly in the summer unless I bump the
octane up to 89. Both run fine on 87 with ambient temps below 100.

"Robert M. Gary" wrote in message
...
On Jun 7, 10:47 pm, wrote:
Due to the problems of getting 100LL in many places, Lycoming is
seeking FAA approval for the standard compression engines to be able
to use 93 octane auto gas. Link to avweb article bellow. Sounds like
good news, since I have an O-360. Maybe airports will start to carry
it.

This is also why owners with constant
speed props are told to always reduce manifold pressure first. If you
are at 800 psi with everything wide open and you reduce rpm you have
made the situation worse. The engine stays at the high pressures
longer, and at a different spot relative to top dead center, because
you just made the engine turn slower. All bad.

Welcome once again to "Amateur Hour".

Funny thing, most of the radial engines I've flown, not to mention GTSIO-520's and TSIO-540's always operate at high MP versus low RPM.

Please show me in a POH where it specifically says "Do not reduce RPM before MP."